The present invention relates to methods and apparatus for optically reading information, and specifically relates to an optical reading apparatus and an optical reading method for obtaining objective information by reading a subject and processing the read information through an arithmetic processing.
Conventionally, when deriving the objective information from optical information read optically, the objective information is detected or recognized by applying a processing-operation, such as an image-analyzing operation, etc., to signals obtained by reading the optical information. For instance, the barcode recognition, the character recognition, the shape recognition, etc. are included in the above operation.
Specifically, noise components caused by an optical mechanism are included in opt-electronic conversion results outputted by the optical reading apparatus, which comprises a light source, a photo-receiving element and a calculating means, and irradiates a light bundle emitted from the light source onto the subject, and opt-electronically converts its reflected light or its transmitted light with the photo-receiving element, and then, detects the information of the subject by applying the an arithmetic processing to the signals converted opt-electronically.
For instance, in case that different kinds of printed patterns or the like exist on the surface of the subject when the light bundle emitted from the light source is irradiated onto the subject to detect a concave or a convex of the surface of the subject with its reflected light, the signals opt-electronically converted by the photo-receiving element include noise components, caused by an optical mechanism, which is overlapped with the concave or convex information as a detecting subject.
As mentioned above, when noise components caused by optical factors is larger than the opt-electronically converted signals, etc., and, for instance, characters and numerals formed in either the convex or the concave are detected/recognized by detecting the aforementioned convex or concave formed on the surface of the subject, and various kinds of patterns printed or residing on the surface of the subject works as noise components caused by optical factors, such the noise components considerably impede an accurate reading action for the information, which include deviations of the convex or the concave as a detecting object.
Incidentally, explaining according to the aforementioned example, in case that the information, being a detecting object of the subject, is at least one of the convex or the concave formed on the surface of the subject, and the noise components caused by optical factors, such as the distribution of reflecting rates or the distribution of transmitting rates, exist on the surface of the subject, when detecting them with a reflected light or a transmitting light, the noise components, caused by such as colors and density patterns, etc., which influences to the reflecting rate or the transmitting rate on the surface of the subject, are integrated with the detected signals including the information of the convex or the concave being the detecting object.
Accordingly, in case that the noise components are the optical information caused by optical factors, when optically reading the information being the detecting object, it has been very difficult to separate both of them or to remove only the noise components from the detected signals.
Conventionally, methods for eliminating fine noises caused by electronic factors or noises, having a frequency of 50-60 Hz and generated by a fluorescent lamp, have been well known. Further, although, other than the above methods, a method for discriminating figures and characters by applying an arithmetic filtering processing to two-dimensional information (image data) thereafter, when the noise components, overlapping with the signals itself generated by the photo-receiving element, are large, it is impossible to accurately detect/recognize the information being a objective detecting object, even if the CPU in the later stage applies an arithmetic processing for its image analysis.
The present invention is attained in view of the abovementioned problems in conventional optical reading apparatus and optical reading methods. In a method and an apparatus, in which objective information are obtained by optically reading the subject and applying arithmetic processing, it is an object of the present invention to reduce the influence of the noise components caused by optical factors and to improve the accuracy of the necessary information being a detecting object.
Accordingly, to overcome the cited shortcomings, the abovementioned object of the present invention can be attained by optical reading apparatus and methods described as follow.
(1) An optical reading apparatus, comprising: a light source to irradiate a light flux onto a subject; a photo-receiving element to receive a reflected light or a transmitted light of the light flux irradiated onto the subject, and to generate signals based on an opt-electronic converting action; an arithmetic processing section to apply an arithmetic processing to the signals, in order to detect information of the subject; and a calculating section to apply a calculating processing, for reducing noise components caused by optical factors, to the signals generated by the photo-receiving element, in order to obtain output signals in which noise components are reduced, before the arithmetic processing section applies the arithmetic processing to the signals.
(2) The optical reading apparatus of item 1, wherein the photo-receiving element is capable of detecting a photo-receiving position, and the optical reading apparatus detects a distribution of deviations of at least one of a convex or a concave on the subject, based on the variation of the photo-receiving position.
(3) The optical reading apparatus of item 2, wherein the noise components caused by optical factors, arises from a distribution of light-reflecting rates or light-transmitting rates of the subject.
(4) The optical reading apparatus of item 3, wherein the calculating section finds a first centroid of the light on the photo-receiving element, and a second centroid of the light on the photo-receiving element, caused by the distribution of light-reflecting rates or light-transmitting rates of the subject, from the signals generated by the photo-receiving element, and the output signals, in which the noise components are reduced, are obtained by applying the calculating processing, for reducing the noise components caused by optical factors, to the signals generated by the photo-receiving element by subtracting the second centroid of the light from the first centroid of the light.
(5) The optical reading apparatus of item 4, wherein the calculating section finds the second centroid of the light from a total quantity of the light on the photo-receiving element.
(6) The optical reading apparatus of item 5, wherein the photo-receiving element is a one-dimensional PSD (Position Sensitive Detector), and the calculating section finds the first centroid of the light from two electronic current values or two voltage values outputted from both ends of the one-dimensional PSD, and the calculating section finds the second centroid of the light from a sum of two electronic current values or two voltage values outputted from both ends of the one-dimensional PSD.
(7) The optical reading apparatus of item 6, wherein the calculating section comprises a memory to store the two electronic current values or the two voltage values outputted from the both ends of the one-dimensional PSD, and the calculating section finds the first centroid of the light from two electronic current values or two voltage values stored in the memory, and the memory also stores the sum of the two electronic current values or the two voltage values, and the calculating section finds the second centroid of the light from the sum stored in the memory.
(8) The optical reading apparatus of item 6, wherein the light flux is irradiated onto the subject while the subject is moving relative to the light flux, and the light flux has a width in a moving direction of the subject or the light flux, and the light on the photo-receiving element has a light-spot width corresponding to the width of the light flux, and the calculating section finds the second centroid of the light from the sum of two electronic current values or two voltage values outputted from the both ends of the one-dimensional PSD, in respect to the light-spot width.
(9) The optical reading apparatus of item 1, wherein the light flux is irradiated onto the subject while the subject is moving relative to the light flux in a moving direction, and the light flux is a linear light being slender in a direction orthogonal to the moving direction.
(10) The optical reading apparatus of item 3, wherein the calculating section finds the noise components caused by optical factors, based on a difference between frequency components of the signals generated by the photo-receiving element.
(11) The optical reading apparatus of item 1, wherein the photo-receiving element is either a PSD, a PD (Photo Diode) or a solid-state imager.
(12) The optical reading apparatus of item 1, wherein the optical reading apparatus detects a distribution of deviations of at least one of a convex or a concave formed on the subject, and the photo-receiving element is a multi-segmented photo-diode, and either a knife edge method, an astigmatism method or a beam-size method is employed for detecting the distribution of deviations of at least one of a convex or a concave formed on the subject.
(13) The optical reading apparatus of item 1, further comprising: an aperture to optically shade the noise components caused by optical factors.
(14) The optical reading apparatus of item 1, wherein a plurality of light sources, each of which is equivalent to the light source, are symmetrically disposed to optically reduce the noise components caused by optical factors.
(15) The optical reading apparatus of item 1, wherein a plurality of photo-receiving elements, each of which is equivalent to the photo-receiving element, are symmetrically disposed, and photo-receiving results outputted from the photo-receiving elements are synthesized or selected to optically reduce the noise components caused by optical factors.
(16) A method for reading optical information, comprising the steps of: irradiating a light flux onto a subject; receiving a reflected light or a transmitted light of the light flux, irradiated onto the subject, with a photo-receiving element; generating signals based on an opt-electronic converting action performed by the photo-receiving element; applying a calculating processing, for reducing noise components caused by optical factors, to the signals, in order to obtain output signals in which noise components are reduced; and applying an arithmetic processing to the output signals, in order to detect information of the subject.
(17) The method of item 16, wherein it is possible to detect a photo-receiving position on the photo-receiving element from the signal, and a distribution of deviations of at least one of a convex or a concave on the subject is detected, based on the variation of the photo-receiving position.
(18) The method of item 17, wherein the noise components caused by optical factors, arises from a distribution of light-reflecting rates or light-transmitting rates of the subject.
(19) The method of item 18, wherein a first centroid of the light on the photo-receiving element, and a second centroid of the light on the photo-receiving element, caused by the distribution of light-reflecting rates or light-transmitting rates of the subject, are found from the signals generated by the photo-receiving element, and the output signals, in which the noise components are reduced, are obtained by applying the calculating processing, for reducing the noise components caused by optical factors, to the signals generated by the photo-receiving element by subtracting the second centroid of the light from the first centroid of the light.
(20) The method of item 19, wherein the second centroid of the light is found from a total quantity of the light on the photo-receiving element.
Further, to overcome the abovementioned problems, other optical reading apparatus and optical reading methods, embodied in the present invention, will be described as follow:
(21) An optical reading method, characterized in that,
in the optical reading method, in which a light source, a photo-receiving element and an arithmetic processing section are included, and information of a subject are detected by opt-electronically converting a reflected light or a transmitted light of the light bundle emitted from the light source in respect to the subject having optical information and by applying an arithmetic processing to opt-electronically converted results,
noise components, caused by optical factors when the photo-receiving element detects the reflected light or the transmitted light of the light bundle emitted from the light source, are reduced by performing an elimination calculating processing as a separate arithmetic processing to be performed before the arithmetic processing.
(22) An optical reading apparatus, characterized in that,
in the optical reading apparatus, which comprises a light source, a photo-receiving element and an arithmetic processing section, and detects information of a subject by opt-electronically converting a reflected light or a transmitted light of the light bundle emitted from the light source in respect to the subject having optical information and by applying an arithmetic processing to opt-electronically converted results, the optical reading apparatus comprises an elimination calculating section for performing an elimination calculating processing as a separate arithmetic processing to be performed before the arithmetic processing to reduce noise components caused by optical factors when the photo-receiving element detects the reflected light or the transmitted light of the light bundle emitted from the light source.
For instance, to discriminate and classify papers based on a reflecting rate of each paper in a factory, etc., in which box-type products made of papers are handled, the intensity of the light reflected from the paper, being an inspection subject, could be measured to discriminate and classify papers. The measurement is performed under a room lamp, a fluorescent lamp in the vicinity or an illuminating light source provided with the photo-receiving element, and the signals outputted from the photo-receiving element are analogue-to-digital converted to store them. In this case, when a shadow portion of a box arrives at the detecting position, the intensity of the received light abruptly decreases at the shadow portion, and it is erroneously determined that the box has a very low reflecting rate. To avoid the above drawback, the information lower than a predetermined light intensity is eliminated by performing logical judgments. Thus, it becomes possible to accurately discriminate the subject.
Accordingly, in the optical reading apparatus of item 22, the optical reading apparatus comprises at least a photo-receiving element, and opt-electronically converts the received light in such a manner that the light reflected from the subject enters into the photo-receiving element under the room lamp, etc., and applies processing, equivalent to mathematic logical calculations, such as a differential calculus, an integral calculus, sum and subtract calculus, etc., to the signals generated by the photo-receiving element or the analogue-to-digital converted and/or amplified signals to find noise components caused by optical factors with simpler arithmetic elements and circuits, and then, obtains the optimum signals by subtracting the noise components, etc.
In other words, the noise components are removed from the original signals being detecting signals at the initial stage, and a binary coding processing is applied to the obtained signals to perform image processing.
(23) The optical reading apparatus cited in item 22, characterized in that the elimination calculating section analogue-to-digital converts photo-electronically converted results to store digital data into a memory, and finds the noise components caused by optical factors from the digital data stored in the memory to reduce the noise components included in the digital data.
For instance, to discriminate and classify papers based on a reflecting rate of each paper, the intensity of the light reflected from the paper, being an inspection subject, could be measured to discriminate and classify papers, as mentioned in regard to items 21-22. In this case, the signals outputted from the photo-receiving element are analogue-to-digital converted to store digital data into a memory, and the arithmetic processing is performed in respect to the data stored in the memory by executing software. As mentioned above, when a plurality of data are stored in the memory and utilized for the arithmetic processing, it becomes possible to analyze a plurality of data with various kinds of method to retrieve many information, and to improve the accuracy of lowering the noise components. Specifically, sometimes, it becomes possible to eliminate noise components, which cannot be separated by means of mechanical methods, by performing complicated arithmetic processing.
In the above simplified example, when the shadow portion arrives at the detecting position, the intensity of the received light abruptly decreases, and therefore, it is erroneously determined that the subject has a very low reflecting rate. To avoid the above drawback, the data lower than a predetermined light intensity is reduced from the stored data at the initial stage of the arithmetic processing by performing logical judgments. In this method, the signals are initially processed to obtain the signals in which the noise components are reduced, namely, the noise components are initially removed from the original signals by calculating with data stored in the memory. Accordingly, since the signals, from which noise components are already removed, are encoded into binary or multivalued data to conduct the image processing, it is possible to precisely detect the information under the detecting operation, and further, the abovementioned method is superior to conventional methods for discriminating a shape or letters by afterwardly applying an arithmetic filtering processing to two-dimensional information stored in advance.
Further, as a concrete example of the configuration, there will be exemplified the apparatus, in which the photo-receiving element is a position detecting element such as a PSD or the like being detectable of the centroid of the received light, and the light source is a Laser Diode (hereinafter referred to as a LD), and the irradiation light is a linear light obtained by shaping the light bundle emitted from the light source, with a cylindrical lens, etc., and the subject is a card-type subject, which moves at a constant velocity and comprises at least one of a concave and a convex. When detecting the convex or the concave in the above situation and the PSD, serving as a photo-receiving element, is apart from the subject, since the light emitted from the light source is a coherent light, a large amount of Fresnel diffraction would occur at, for instance, edges of optical members, such as a supporting member of the optical system, an aperture member, etc., which would shade the optical path. This Fresnel diffraction generates noise components, which disturbs the distribution of incident light entering into the PSD, etc. More accurate measurements can be achieved by finding Fresnel diffraction components from the length of the optical path and the distribution of luminous intensity, etc., and finding the noise components onto the PSD, caused by the Fresnel diffraction components, and applying the arithmetic processing to the signals detected by the PSD so as to reduce the noise components.
Incidentally, the Fresnel diffraction possibly occurs, even when the subject is transparent. For instance, when it is intended to accurately reading positions of characters or symbols formed on transparent subject 102, as shown in FIG. 23, a large amount of Fresnel diffraction are generated by shaping the light bundle emitted from LD 9 to irradiate the shaped light onto transparent subject 102, and impede an accurate operation for reading the positions of small characters or symbols. Accordingly, the Fresnel diffraction components, which is a function of distance L between the subject and PD array 104, are calculated from the signals outputted by PD array 104 (or the CCD sensor or the PSD), and accurate information can be obtained by subtracting the calculated Fresnel diffraction components from the output signals of PD array 104.
(24) The optical reading apparatus cited in item 22 or item 23, characterized in that, the information of the subject, being a detecting object, is information in respect to at least one of the concave and the convex on the surface, and the noise components caused by the optical factors arise from the distribution of light-reflecting rates or the distribution of light-transmitting rates.
Incidentally, when the information of the subject, being a detecting object, is information in respect to at least one of the concave and the convex on the surface, and the noise components caused by the optical factors arise from the distribution of reflecting rates or the distribution of transmitting rates due to the density variation on the surface of the subject (a pattern having color contrast, a pattern having different colors, such as black and white, etc., etc.), it is difficult to discriminate between the optical information detected from at least one of the concave and the convex on the surface of the subject and the optical information detected from the density variation on the surface of the subject. However, the accuracy of the necessary information, being a detecting object, can be improved by performing the elimination calculating processing in the configuration of item 21 or item 22 before performing the arithmetic processing to reduce the influence of the noise components caused by optical factors.
(25) The optical reading apparatus cited in any one of items 22-24, characterized in that, the noise components caused by optical factors are detected based on differences between frequency components of the photo-electronically converted results.
Incidentally, when the information of the subject, being a detecting object, is information in respect to at least one of the concave and the convex on the surface, and the noise components caused by the optical factors arise from the distribution of reflecting rates or the distribution of transmitting rates due to the density variation on the surface of the subject, it is difficult to discriminate between the optical information detected from at least one of the concave and the convex on the surface of the subject and the optical information detected from the density variation on the surface of the subject. Further, the noise components emerge in response to the width pitch of the pattern and sometimes indicate movements, which would be resolved into the frequency domain, such as strengthening or weakening, etc. Accordingly, the accuracy of the necessary information, being a detecting object, can be improved by detecting the noise components based on the differences between frequency components of the optical information when performing the elimination calculating processing in the configuration of item 21 or item 22 before performing the arithmetic processing to reduce the influence of the noise components caused by optical factors.
(26) An optical reading method, characterized in that,
in the optical reading method, in which a distribution of deviations of at least one of a convex or a concave, recorded on a subject, is detected by the steps of irradiating a light bundle emitted from a light source onto the surface of the subject, guiding the light reflected from the surface of the subject to a photo-receiving element being capable of detecting a receiving position of the reflected light, and applying an arithmetic processing, for finding a centroid of the reflected light, to the signals photo-electronically converted by the photo-receiving element,
the distribution of deviations of at least one of the convex or the concave, recorded on the subject, is detected by the steps of finding the centroid of the reflected light caused by a distribution of reflecting rates of the subject, and subtracting the centroid of the reflected light caused by a distribution of reflecting rates of the subject from the centroid of the reflected light found from the signals photo-electronically converted by the photo-receiving element.
(27) An optical reading apparatus, characterized in that,
in the optical reading apparatus, in which a distribution of deviations of at least one of a convex or a concave, recorded on a subject, is detected by the steps of irradiating a light bundle emitted from a light source onto the surface of the subject, guiding the light reflected from the surface of the subject to a photo-receiving element being capable of detecting a receiving position of the reflected light, and applying an arithmetic processing, for finding a centroid of the reflected light, to the signals photo-electronically converted by the photo-receiving element,
the distribution of deviations of at least one of the convex or the concave, recorded on the subject, is detected by the steps of finding the centroid of the reflected light caused by a distribution of reflecting rates of the subject, and subtracting the centroid of the reflected light caused by a distribution of reflecting rates of the subject from the centroid of the reflected light found from the signals photo-electronically converted by the photo-receiving element.
Generally speaking, in the operation for optically reading the information with the reflected light, the variation of reflecting rates on the surface of the subject caused by the information, being different from the information of the detecting object, could be the cause of a big confusion in respect to the information of the detecting object. Specifically, when other signals (quasi-signals), the amplitude of which is equivalent to or larger than that of the original signals to be obtained, is outputted from the photo-receiving element in a state of overlapping each other, it is virtually impossible to eliminate the quasi-signals in advance only by its mechanism and/or optical configuration. It becomes possible, however, to reduce the noise components, disturbing as the quasi-signals, by performing the steps of storing the signals outputted from the photo-receiving element into a memory, deriving the information in regard to the variation of reflecting rates on the surface of the subject in an arithmetic processing operation, and removing the information from the signals outputted from the photo-receiving element. Incidentally, the arithmetic processing operation, performed in this case, is a kind of simulation calculating operation.
An apparatus, in which the photo-receiving element is a position detecting element, such as the PSD, etc., being capable of detecting the centroid of the received light, the light source is the LD (Laser Diode), the illumination light is a linear light formed by shaping the light bundle emitted from the light source with a cylindrical lens, etc., the subject is a card-type subject, which moves at a constant velocity and comprises at least one of a concave and a convex, and the PSD can receive the linear light corresponding to the convex or the concave projected on the PSD, is assumed as a concrete example. Incidentally, when a one-dimensional PSD is employed for the PSD serving as a photo-receiving element, two electronic currents can be outputted from the both ends of the photo-receiving element. In this case, it is possible to derive the centroid position of the light received on the PSD from the arithmetic processing of the value, obtained through the processes of the I/V conversion, the amplifying operation and the A/D conversion of the two electronic currents. Further, by image-processing the information of the centroid position by means of a processing device such as a computer, etc., and recognizing the information as the convex or the concave, it is possible to distinguish the information of characters, numerals, etc. formed in either the convex or the concave by embossing the subject.
In other words, it is possible to obtain the accurate optical information of at least one of the convex or the concave, in which the noise components are reduced, by calculating the centroid position of the light in respect to the noise components, serving as quasi-signals, from the optical information in proportion to the distribution of reflecting rates, and by subtracting the centroid position of the light in respect to the noise components from the information of the centroid position of the light, which is initially found from the light received on the PSD by directly applying the arithmetic processing.
(28) The optical reading apparatus cited in item 27, characterized in that, the photo-receiving element is either a PSD, a PD (Photo Diode) or a solid-state imager.
In the abovementioned optical reading apparatus, the outputs of the photo-receiving element in a time passage domain are in proportion to the distribution of reflecting rates of the subject, and it is possible to conduct the aforementioned subtracting operation based on the information of the outputs of the photo-receiving element stored within a short time. Therefore, it becomes possible to complete the arithmetic processing more quickly than in the method of finding the distribution after storing all of the information in the memory.
(29) The optical reading apparatus cited in item 24 or item 25, characterized in that, the information is detected by employing a multi-segmented photo-diode for the photo-receiving element and by applying any one of a knife edge method, an astigmatism method, a beam-size method or a combination of them.
In the abovementioned optical reading apparatus, the laser beam is focused onto the subject, and the light diffused and reflected from the subject is collected and guided to the multi-segmented photo-diode. Then, the distance relationship between the subject and the multi-segmented photo-diode is determined based on the difference between the outputs of photo-segments included in the multi-segmented photo-diode. When the distribution of reflecting rates caused by the density contrast resides on the surface of the subject, the calculation result for the abovementioned difference information falls into disorder. However, since the sum of the output values of photo-segments included in the multi-segmented photo-diode is equivalent to the distribution of reflecting rates, it becomes possible to remove the noise components caused by the density contrast of the subject from the output of the multi-segmented photodiode by utilizing the sum of them.
(30) The optical reading apparatus cited in any one of items 22-25 or items 27-29, characterized in that, an aperture member, which optically shades the noise components caused by optical factors, is disposed.
In the abovementioned optical reading apparatus, the aperture member is disposed at anywhere in the light path, in order to prevent the noise components caused by optical factors from entering into the photo-receiving element, or in order to reduce the amount of the noise components entering into the photo-receiving element. Further, specifically, when the photo-receiving area on the photo-receiving element is reduced by optimally disposing the aperture member, it is possible to reduce the low frequency noise components outputted in the time passage domain and which belong to the noise components caused by the optical factors. As mentioned above, by adjusting the light entering into the photo-receiving element, it becomes possible to remove the noise components having frequencies lower than a predetermined frequency.
(31) The optical reading apparatus cited in any one of items 22-25, characterized in that, a plurality of light sources are symmetrically disposed to reduce the influence of the noise components caused by the optical factors.
In the above optical reading apparatus, a plurality of light sources are symmetrically disposed to cancel the noise components caused by the optical factors with each of the light, and as a result, the influence of the noise components is suppressed.
(32) The optical reading apparatus cited in any one of items 22-25, characterized in that, a plurality of photo-receiving elements are symmetrically disposed, and the influence of the noise components caused by the optical factors is reduced by synthesizing or selecting the photo-receiving results of the plurality of photo-receiving elements.
In the above optical reading apparatus, a plurality of photo-receiving elements are symmetrically disposed, and the photo-receiving results of the plurality of photo-receiving elements are synthesized or selected to cancel the noise components caused by the optical factors, and as a result, the influence of the noise components is suppressed.